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import skdb
from skdb import Part, Interface, Unit, UnitError
from string import Template
threads = skdb.load_package('threads')
Thread = threads.Thread
__author__ = "ben lipkowitz, bryan bishop"
__license__ = "GPL"
__version__ = "0.0.1"
__maintainer__ = "ben lipkowitz"
__email__ = 'no thank you, sir'
__status__ = "Development"
class Screw(Part):
yaml_tag = "!screw"
'''a screw by itself isn't a fastener, it needs a nut of some sort'''
##i suppose this stuff should go in a screws.yaml file or something, along with standard diameters
proof_load = {#grade:load
'1':'33ksi',
'2':'55ksi',
'3':'85ksi',
'5':'85ksi',
'7':'105ksi',
'8':'120ksi',
}
tensile_strength = {#grade:load
'1':'60ksi',
'2':'74ksi',
'3':'110ksi',
'5':'120ksi',
'7':'133ksi',
'8':'150ksi',
}
def __init__(self, thread=None, length=None, grade="2", name=None):
'''length is defined as the distance from bottom of the head for all screws but
flat head and set screws which use the top of the head instead'''
#thread.__init__()
self.thread, self.length, self.grade, self.name = thread, length, grade, name
if self.thread and self.length:
if self.thread.length is None: self.thread.length = self.length
assert self.length.compatible('m') #this sort of thing should go in a generic unit-checker function
#is it right to define these interfaces here, instead of in the thread object?
thread_loosen = Interface("thread-loosen", part=self)
thread_tighten = Interface("thread-tighten", part=self)
compression_face = Interface("compression-face", part=self)
torque_spline = Interface("torque-spline", part=self)
if thread == None: raise ValueError
#the following if should be commented out when skdb/core/threads.py Thread interfaces is fixed
#if thread.interfaces == None or len(thread.interfaces) == 0:
thread.interfaces = [thread_loosen, thread_tighten]
if len(thread.interfaces) > 0:
#if the thread already has interfaces with name "thread_loosen"/"thread_tighten", use them.
thread_loosen = thread.interfaces[0] #FIXME: this is very, very wrong
thread_tigthen = thread.interfaces[1] #FIXME too.
self.interfaces = [thread_loosen, thread_tighten, compression_face, torque_spline]
self.check_compatibility()
def check_compatibility(self):
#shouldnt this function be in thread.py?
for (k,v) in {'pitch': 'rev/in', 'diameter': 'in', 'tensile_area': 'in^2'}.items():
parameter = getattr(self.thread, k)
try:
Unit(parameter)
assert (getattr(self.thread, k)).compatible(v)
except UnitError, e:
#ok it's not a Unit object
#and instead a method in the Thread class
res = parameter()
assert res.compatible(v)
#note these tables vary from source to source; might want to check if it really matters to you
def max_force(self):
'''load screw can withstand without permanent set, in lbf'''
s = Template('$area*$strength')
string = s.safe_substitute(area=self.thread.tensile_area(), strength=Screw.proof_load[self.grade])
return skdb.Unit(string).to('lbf')
def breaking_force(self):
'''load screw can withstand without breaking, in lbf'''
s = Template('$area*$strength')
string = s.safe_substitute(area=self.thread.tensile_area(), strength=Screw.tensile_strength[self.grade])
return skdb.Unit(string).to('lbf')
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